1. Field of the Invention
The present invention relates to valve timing adjuster that adjusts valve timing of opening and closing at least one of an intake valve and an exhaust valve.
2. Description of Related Art
A conventional vane-type valve timing adjuster is known to drive a camshaft in order to open and close at least one of an intake valve and an exhaust valve of an internal combustion engine. More specifically, the conventional valve timing adjuster drives the camshaft by using the drive force obtained through a timing pulley or a chain sprocket that is rotatable synchronously with a crankshaft of the engine. Also, the conventional valve timing adjuster opens and closes the valve based on a rotational phase difference between (a) the camshaft and (b) the timing pulley or the chain sprocket.
In the above conventional vane-type valve timing adjuster, a vane rotor having vanes slides on longitudinal end surfaces of a housing member that rotationally receives therein the vane rotor. Thus, it is required to provide a slide clearance between the vane rotor and the housing member. The slide clearance is designed to be very small. However, it is impossible to sufficiently prevent pressurized oil in the hydraulic chamber from leaking through the slide clearance.
The slide clearance includes a radial clearance and a thrust clearance, for example. The radial clearance is defined between the vane rotor outer periphery and the housing member inner periphery. The thrust clearance is defined between the axial end surface of the vane rotor and the axial end surface of the housing member. In the present specification, the thrust clearance is focused on as the slide clearance. It should be noted that the leakage through the radial clearance has already been addressed by components, such as a conventional “seal member 7” and a conventional “leaf spring 8”, as shown in the embodiments of the present invention.
In the present specification, leakage (or unwanted communication) of pressurized oil between an advance hydraulic chamber and a retard hydraulic chamber is referred to as “internal leakage”. When the internal leakage occurs, pressurized oil supplied by an oil pump for valve timing adjustment is not effectively utilized. Thereby, energy efficiency of the oil pump may degrade disadvantageously, and also accuracy of a phase control through the adjustment of the valve opening/closing timing may also deteriorate disadvantageously.
In order to deal with the above disadvantages, in the invention disclosed by JP3567551 or JP-A-H11-62524, a sealing sheet is provided between the vane rotor and the gear, and the sealing sheet has a projecting resilient part. Thus, it is possible to prevent leakage of pressurized oil from the hydraulic chamber.
FIGS. 9A and 9B show a sealing sheet 150 described in JP-A-H11-62524. The sealing sheet 150 includes a fitting hole 152, through holes 151, and a pressurized oil introduction passage 153. The fitting hole 152 is fitted with the end portion of the camshaft. The through holes 151 are used for positioning the sealing sheet 150 in the circumferential direction. The pressurized oil introduction passage 153 is configured to introduce pressurized oil from one of the advance hydraulic chambers to the back side of the sealing sheet 150. Also, a resilient part 155 that is a disc spring is formed around a radially innermost part 154 of the sealing sheet 150. When the sealing sheet 150 is provided between the vane rotor and the gear, the resilient part 155 is bent, and the sealing sheet 150 contacts the vanes of the vane rotor. Furthermore, when pressurized oil is introduced to the back side of the sealing sheet 150 through the pressurized oil introduction passage 153, a differential pressure across the sealing sheet 150 is generated. Thus, the differential pressure urges the sealing sheet 150 toward the vane from the back side in order to prevent leakage of pressurized oil through the slide clearance.
In the present specification, sealing performance for limiting the “internal leakage” is referred to as “internal leakage sealing performance”.
The sealing sheet 150 described in JP-A-H11-62524 has the resilient part 155 provided only around the radially innermost part 154. Thus, the above sealing sheet 150 is capable of applying the resilient force only to the narrow area. Also, the differential pressure is applied only to the narrow area. As a result, it is impossible to obtain sufficient “internal leakage sealing performance” disadvantageously. Also, because load of the resilient force is concentrated on a particular local spot of the sealing sheet 150, durability of the sealing sheet 150 may become insufficient.
The “sealing sheet 150” described in JP-A-H11-62524 corresponds to a “seal plate” in the present invention.